The present invention relates to a process for the preparation of polymers. In a further embodiment the present invention relates to a process for preparing grafted derivatives of rubbery spine polymers. The processes of the invention utilize bisquinone peroxides that decompose to produce beneficial phenolic derivatives. Moreover the use of the present bisquinone peroxides achieves improved grafting efficiency in the preparation of graft polymers.
It is previously known in the art to obtain grafted rubbery polymers by polymerizing graft forming polymerizable monomers in the presence of a rubbery spine polymer. The use of rubbery spine polymers comprising in polymerized form conjugated dienes proceeds relatively easily even in the absence of graft promoting additives. The presence of a peroxide free radical initiator is often employed to obtain the polymerization of free radically polymerizable monomers. However, in the use of certain other rubbery spine polymers particularly such polymers that are substantially devoid of ethylenic unsaturation such as alkyl acrylate based rubbery polymers and copolymers of ethylene propylene and optionally a nonconjugated diene (EPDM) rubbers, the grafting efficiency is greatly reduced.
It is previously known in the art to use singlet oxygen generated in situ to promote grafting of graft forming polymerizable monomers onto rubbery spine polymers. Examples of such techniques are contained in U.S. Pat. Nos. 3,484,353, 3,846,266, and 4,717,741. In these references singlet oxygen is photochemically generated and contacted with the rubbery spine polymer prior to contacting the rubbery spine polymer with the graft forming polymerizable mixture. The singlet oxygen generated in situ according to the disclosures of the above referenced patents acts as a graft promoting additive in the polymerization to induce graft formation between the rubbery spine polymer and the matrix polymer. Disadvantageously these methods have involved cumbersome reaction conditions to photogenerate the oxygen in situ. Also such techniques generally employed a photosensitizer, which if not removed from the resulting product, may adversely affect the weatherability and UV light resistance of the resulting polymer.
It is additionally previously known in the art to utilize aliphatic and aromatic peroxide compounds as free radial initiators in polymerization processes. Generally upon heating such peroxides cleave at the oxygen-oxygen bond to form two alkoxy radicals that initiate the free radical polymerization process. Disadvantageously, such free radical forming initiators are generally less effective in obtaining graft polymerization in highly saturated rubber formulations, for example in the preparation of polymers containing the aforementioned EPDM or acrylate rubbers, than in formulations containing conjugated diene based rubbers such as polybutadiene.
Modern thermoplastic resins for use as molding resins often incorporate additives to prevent polymer degradation. Particularly useful are antioxidants such as hindered phenolic compounds, which are usually added in small amounts before or after polymerization. It would be desirable if it were possible to provide a polymerization initiator the decomposition products of which impart improved polymer properties. It would be particularly desirable to provide a polymerization initiator the decomposition products of which comprise a hindered phenolic compound.
It would be desirable if there were also provided an improved process particularly adapted for preparing graft interpolymers of rubbery spine polymers providing improved grafting efficency.